Conventionally, a plurality of insulated wires are used in a vehicle such as an automotive vehicle. The insulated wires are usually bunched into a wiring harness. In a case where some of the insulated wires in the wiring harness are connected together, they are connected such that insulators of the insulated wires are first stripped off to expose conductors inside the insulators and then the connection is established with the conductors in contact with each other using a connection method such as welding and crimping.
Recently, as the method for connecting electric wires, an ultrasonic welding method has been often used considering its easy operation and reliable connecting capability.
For example, an ultrasonic welding method is disclosed in Japanese Patent Application Unexamined Publication No. 2005-322544, by which insulated wires are connected together by bunching them together and stranding exposed conductors of the insulated wires and then welding a stranded portion of the exposed conductors.
Another ultrasonic welding method is disclosed in Japanese Patent Application Unexamined Publication No. Hei 09-155573, by which insulated wires are connected together by interposing a resin between conductors of the insulated wires which are subjected to ultrasonic welding and then welding the conductors together, and at the same time, the resin is made to invade between the conductors, whereby connection strength between the insulated wires is improved.